The purpose of this study is to develop another system (urinary bladder) which can be used for comparison with the trachea on the problem of reversal of preneoplasia with vitamin A analogs (retinoids). The scope of this study encompasses: (1) Development of an organ culture system for the rat urinary bladder, (2) Production of preneoplastic lesions in rat urinary bladders and (3) Assay of the effect of retinoids on preneoplastic lesions in rat urinary bladder in organ culture.